Single spindle and multiple spindle automatic bar machine tools are examples of machines which require elongated bar stock to be fed to the machine tool intermittently. The bar stock is gripped in a collet in the spindle and rotated so that the end of the bar may be cut into the shape desired and then cut off. Next the collet is opened and the bar stock is fed forwardly to engage a stock stop and then the collet is closed ready for the next cycle of operation. This feed forward of the bar stock might be only a small amount if small length parts are being machined or may be a long length if long parts are being machined. The prior art machine tools have known various forms of mechanisms to provide this adjustable length bar feed. One of the earlier arrangements was to use a cam drum within the machine tool and to have a supply of stock feed cams on hand which could be interchangeably fastened on the cam drum. In this way a stock feed could be selected and secured to the cam drum which would provide a stock feed only slightly greater than that actually required for the workpieces to be successively machined. One would have needed an infinite number of such stock feed cams in order to achieve an infinitely adjustable stock feed. Since as a practical consideration this was not possible the machine tool user generally had about six or eight cams of graduated lengths, for example, for a maximum of seven inches of stock feed and a minimum of one-inch of stock feed. If the machine tool user had a part to be machined which was 1.1 inches long then he had to use the next longer cam, for example, one of two-inch stock feed, which meant that the stock feed fingers or pusher fingers would slide on the surface of the bar stock for 0.9 inches of length and this would often mar the surface finish or it would cause undue stress on the stock stop because the rear stock was moving forward rapidly at the time it struck the stock stop.
Other manufacturers used some additional mechanism in series after this first cam drum. The first cam drum still gave a fixed length of stroke but then through interconnected levers with a variable interconnection point or another cam with a changeable angle thereon, an adjustable length of stroke to the stock pusher was achieved. The disadvantages of these arrangements were the added complexity with more mechanism causing more lost motion, more mechanism needing to be manufactured by the machine tool manufacturer and also needing adjustment at the time of changing of the stock feed length.
Accordingly the problem to be solved is how to achieve an adjustable bar stock feed mechanism which would be infinitely adjustable, easy to manufacture and adjust and one which has a constant maximum forward feed position regardless of the amount of feed.